Traditionally, large mechanical type routers have been used, disposed between one or more input fibres and one or more output fibres. The routers may be actuated by electrical motors or solenoids. Such routers are both bulky and expensive, and alternative integrated optical routers have been proposed.
One integrated approach involves fabricating waveguides in a planar substrate, each waveguide being coupled to a corresponding optical fibre. Disposed in the waveguides are phase shifting components which are electrically actuable to change the optical properties of the waveguide material. This may block the transmission of light through a waveguide and or may cause the light to be coupled to an adjacent waveguide. Such a router is described in U.S. Pat. No. 6,028,552.
Another approach to providing an integrated optical router is to provide a linearly movable switching “plate” in a planar substrate between input and output waveguides formed in the substrate. The plate is moveable as a result of electrostatic force. In a first position, a waveguide formed in the plate may couple corresponding input and out waveguides on the substrate, whilst in a second position the waveguide in the plate is misaligned with the input and output waveguides such that they are not coupled together. Such devices operate generally as on off switches, i.e. their capacity to route signals (i.e. from a single input to one of several outputs) is limited.